The performance of the 2 tumor markers carbohydrate antigen 19-9 (CA19-9) and tumor M2 pyruvate kinase (Tu-M2-PK) separately and in combination detecting pancreatic ductal adenocarcinoma (PDAC) was evaluated in a prospective study.The study comprised 103 patients referred because of suspicion of pancreatic cancer. Of these, 51 patients had their conditions diagnosed as PDAC, whereas this diagnosis was ruled out in 52 after 12 months of follow-up. The performance of Tu-M2-PK was compared with that of CA19-9 using cutoff values 15 and 37 U/mL, respectively.The sensitivity of Tu-M2-PK and CA19-9 in detecting PDAC was 55% and 86% at specificities of 52% and 73%, respectively. The area under the curve (AUC) of Tu-M2-PK was 0.55 and that of CA19-9 was 0.84. Combining the 2 markers did not significantly improve AUC (AUC = 0.85, P = 0.72) compared with CA19-9 when used alone. The presence of chronic pancreatitis or jaundice causes increased levels of CA19-9 but does not influence Tu-M2-PK.Tu-M2-PK was inferior to CA19-9 as marker of PDAC. Tu-M2-PK may have a role in diagnosing PDAC because it is not affected by cholestasis or Lewis phenotype. Neither tumor marker can stand alone in the diagnosis of PDAC.